Relevance of Research Plan: One priority area for the Department of Veterans Affairs (DVA) is to provide quick, effective, recovery-oriented treatments for depressive/anxiety disorders, representing the most common and impairing psychiatric disorders in Veterans. Cognitive behavioral therapy (CBT) has demonstrated reliable efficacy in treating depressive/anxiety disorders and their related impairments as well as encouraging social reintegration. However, CBT is underutilized due in large part to the complexity and number of disorder-specific treatments (DSTs) across disorders, as well as extensive training needed to apply them to different diagnoses as well as different diagnoses with different comorbidities. In addition, the focus of DSTs and their requirement to segregate patients by disorder limit the use of group CBT in the DVA and its established benefits to patient access and social reintegration. Recently, Transdiagnostic Behavior Therapy (TBT) was developed in the DVA to address overall psychiatric well-being and rehabilitation in Veterans, without limiting treatment to a single psychiatric diagnosis. Initial studies of TBT show the treatment is effective in reducing impairment across multiple domains of functioning, including health and diet, work and financial situation, recreation and community involvement, and social and family relationships in Veterans presenting with a wide range of diagnoses, including depressive disorders, anxiety disorders, PTSD, and related comorbidities. In addition, a recent study demonstrated that TBT could be easily disseminated to DVA providers and implemented with DVA patients. Although additional study is needed, the transdiagnostic approach in TBT, including a newly developed Group TBT (G-TBT), may address many of the current limitations of the DSTs and lead to improved outcomes for Veterans with PTSD and/or depression. Primary Aims in Research Plan: The proposed study aims to: 1) test equivalence of G-TBT and Group DSTs (G-DSTs) in improving impairment and social reintegration as well as reducing psychiatric symptomatology, and 2) compare the access, feasibility, and acceptability of G-TBT and G-DSTs. Participant population: The participants of the proposed study will include 208 DVA patients with PTSD and/or major depressive disorder. Procedures to be used: A randomized controlled trial (RCT) with G-TBT and G-DSTs conditions will be completed. Participation in the RCT will involve completion of: 1) consent documentation, 2) intake assessment, 3) random assignment to treatment condition, 4) weekly 90-minute appointments of group psychotherapy for 12 weeks, and 5) self-report assessments of quality life, social reintegration, and psychiatric symptomatology at intake, mid-treatment, post-treatment, and 6-month follow-up. Anticipated Impacts on Veterans Health Care: Upon investigation with supported efficacy and non- inferiority as compared to G-DSTs, G-TBT will represent an excellent treatment option within the DVA in terms of providing a single group protocol that is easy to disseminate to and implement by providers as well as being efficacious in addressing functional impairment, social reintegration, and psychiatric symptomatology and with improved access for Veterans with various depressive/anxiety disorders and related comorbidities.